1. Field of the Invention
The present invention relates to an engine control apparatus having a function of cutting off a supply of fuel to a misfired one of cylinders of an engine when a rise in temperature of exhaust gas resulting from a misfire of the engine is assumed to damage a catalyst.
2. Description of the Related Art
A conventional engine control apparatus is equipped with a fuel injection amount setting means for setting a fuel injection amount in accordance with an operational state of an engine, an exhaust gas temperature abnormal rise detecting means for detecting an abnormal rise in temperature of exhaust gas, a misfired cylinder determining means for determining a misfired cylinder when the exhaust gas temperature abnormal rise detecting means has detected an abnormal rise in the temperature of exhaust gas, and a fuel supply cutoff means for cutting off a supply of fuel to the misfired cylinder determined by the misfired cylinder determining means.
When the temperature of exhaust gas has exceeded a first set temperature set in advance in accordance with an engine rotational speed, the exhaust gas temperature abnormal rise detecting means determines that the temperature of exhaust gas has risen abnormally, and cuts off the supply of fuel. At this moment, the fuel injection amount setting means sets the fuel injection amount to a base fuel injection amount, thereby prohibiting the fuel injection amount from being enriched.
The fuel supply cutoff means cancels the cutoff of the fuel supply (hereinafter referred to as “makes a recovery from the cutoff of fuel supply”) when the temperature of exhaust gas has become equal to or lower than a second set temperature set in advance (e.g., see JP 2001-20792 A).
In the aforementioned conventional apparatus, the supply of fuel is cut off on a condition regarding the temperature of exhaust gas, so a recovery from the cutoff of the fuel supply cannot be made in consideration of the operational state of the engine.
Thus, the recovery from the cutoff of the fuel supply is made in a high load region which causes damage to a catalyst, so a large amount of unburnt fuel may be allowed to flow into the catalyst.
Even when a misfire occurs due to a transient cause such as insufficient combustion at low temperatures, the cutoff of the fuel supply is continued until the temperature of the exhaust gas becomes equal to or lower than the second set temperature set in advance.
In the conventional engine control apparatus, a large amount of unburnt fuel maybe allowed to flow into the catalyst. Therefore, the temperature of the catalyst rises abruptly to reach an abnormally high temperature, so there is caused a problem in that the catalyst is damaged.
A temperature sensor also needs to be provided to detect a temperature of the exhaust gas, so there is also caused a problem of a rise in cost.
Even when a misfire occurs due to a transient cause, the cutoff of the fuel supply is continued until the temperature of the exhaust gas becomes equal to or lower than the second set temperature set in advance. Therefore, in the case of a four-cylinder engine, the engine is operated with only three cylinders being supplied with fuel. As a result, there is also caused a problem in that a desired output cannot be obtained.